Improvement in oieculak saws



@atten tetra @anni @fitta IMPROVEMENT IN CIRCULAR SAWS.

"dlgs Segnale nfernh tu in tiges@ @tritata ntnrt mit mating gaat nf the samt.

TO ALL WHOM IT MAY CONGERN:

Be it known that I, H'ENRY DISSTON,of lhiladelphia, Pennsylvania, havey inventedl an Improvement in Circular Saws; and I do hereby declare the following to be a full, clear, and exact description of the same.

My invention consists of a circular saw,`the teeth of which are shaped for bein-g sharpened, in the manner described hereafter, so that the said teeth maybe cut awayto any extent which proper sharpening may'require, without removing the saw from its spindle, or without reducing it in diameter to the extent-necessary in sharpening the teeth of ordinary saws. f

In order to enab'le others skilled in the art to make my invention, I will new proceed to describe the construction of the same, reference being had to the accompanying drawing, which forms a part of this specification, :and in whiehl I Figure 1 represents sufficient of a circular saw to illustrate my improvement.

Figure 2,11. diagram illustrating my invention.

Figure 3, a plan view oi' an instrument which may be used for sharpening the teeth; and

Figures 4, 5, and 6, further diagrams illustrative cf, myinvcntion.

A, iig. 1, represents part of a circular saw, and a a1 a2 a3 a* are five of the teeth, the edge y of each of which must be in the areof Na circle, while the front edge a may be curved, and bevelled to a sharp cuttingedge at the point', When thepoints of the teeth have been worn away, they are sharpened 4by filing or otherwise cutting away'the front edge :c of each tooth, until a new point is formed, a cutting-tool of such a character being employed that the precise shape of the front edge is preserved, while the tool is so guided that the relative positions of the two edges x and y are never altered, whatever may be the extent to which the tooth is cut away. For instance, supposing that the tooth a3, in order to be sharpened, has to be cut away from :v to t, lig. 1, an instrument similar to that shown in fig. 3 may be used, the cylindrical tile A corresponding to the shape of the front edge of the tooth, and the bar F coming incontact with the front edge of the tooth a, when the tooth a3 has been filed away to the lirte t, while the strip G, resting on the top of the tooth, guides the file, so that it 'cannot out deeper than the line s. This instrument is more fully described in a separate application vfor a patent, led by me May 30, 1867. In'asmuchas this line s (which, as the front of the tooth is removed, forms a eontinuationot` the bach ofthe tooth 11",) is determined by theback of thetooth a3, as a guide for the instru` ment, this line must be in the are ot" a circle, having the same cent1-eas that from which the back of the tooth a? is drawn, and thus, as the saw is sharpened, the extent to which one tooth is out away is determined by the tooth previously cut, while the form ofthe continuation ofthe back ofthe t'ooth to be next cut in front is determined by the back of the tooth, the front of which is being out away. l

Owing to these peculiarities in the form of the teeth, the'rrelative,positions ofthe front and back edges can never bc altered by sharpening them as above described, although the teeth must of necessity become shorter as the saw is reduced in diameter. This will be readily seen on reference to thevdiagram, g. 2, where the lines X indicate the outlinesoi` the original teeth, th'c lines Y the outlines when each tooth has been cnt away to the extent indicated, andthe lines Z the outline ofthe saw when the teeth have been still further cut away. i

The advantages of my improvement will be best observed by comparing the teeth in iig. 1 with the ordinary saw-teeth, which arc made of different shapes, hut have never been made of' such a form that, in sharpening one tooth, its hack will serve as a guide to determine the shape of the continuation of the bacli of the tooth which is about to be sharpened. In iig. 5, for instance, are represented teeth of a common for-1n, to sharpen 'which involves the necessity of the removal cfal considerable amount of metal, and a great decrease in the diameter of the saw, whereas, in sharpening. the teeth in iig. 1, all that is necessary is to remove a small portionv of the front of one tooth by the guided ileor other equivalent instrument, this sharpening being effected with the removal of'a very small amount of metal, compared with that removed in sharpening ordinary teeth; hence my improved saw will-not only last much longer, but will require less labor and time to maintain in a sharpened condition, with a less reduction in diameterthan saws with ordinary teeth.

The sharpening of my improved saw can also be effected without removing it from its bearings, whereas ordinary saws have frequently to be' removed, and sent a. great dis-tance, toa manufacturer, in order to be sharpa 'ened by'cutting or punching pieces from the plate.

It will be seen that these important ends can only be accomplished by a proper regard to the shape ,and

equality of the teeth iirst eut, for upon these teeth depends the accuracy of the subsequent sharpening of the teeth, and the maintaining of the saw in a true circle, concentric with its spindle, and having teeth of equal size. The first teeth can be easily determined in the following manner: Let m, iig. 6, represent :t portion of the circumference of the steel plate from which the saw has to be made, and n aline concentric with the circumference, and determining the depth to which the teeth must be cut. The circumference is divided into th'e desired number of teeth, the radial lines u representing the fronts of the cutting-points, from which curves c may be formed to represent the fronts of the teeth, these curves being limited by the line n. The backs ol` the teeth can now be determined by describing the are of a circle from the point where the curve e, representing the front of one tooth, touches the line n, to the point 'w of the next tooth. The back of each tooth must in all euses be in the are of a circle, (no other curve will answer the purpose,) drawn from. a point eccentric with the 'centre of rotation ofthe saw. Thus, in fig. 2, the back edge of the tooth g is in the arc of a circle, drawn from the point p, and every tooth in the saw is formed-in a sinnilar manner, so that the sharpening of the teeth may be effected by a reduction of the front edges in spiral courses. It will be understood that it is not absolutely necessary that the front of the tooth should be curved. 4 uw, I claim as my invention, and desire to secure by Letters Patent- A circular' suiv, every tooth of which has its back edge so formed in the are of a circle, having a. centre `eccentric with the centre-ot` rotation ofthe saw, that the sharpening of each tooth may be effected by reducing the front edge in a spiral course, as herein set forth.

In testimony whereof, I have signed my name to this specification in the presence of two subscribing witnesses,

HENRY DISSTON.

Witnesses:

C. E. FOSTER,

W. J. R. DELANY. 

